I played a little game with this car. On the two or three occasions when I took on a new passenger, I would allow about ten minutes to go past without comment as various flutterings of enthusiasm filled the cabin: "Ooh, this is lovely, how wonderful, what a great car, aren't you lucky to have your job, gosh, golly, crumbs, well I'll go to the foot of our stairs," and so on. And then, timing the thing to a nicety, I'd quietly utter the words which would have such a devastating effect: "Of course, it's also a diesel."In the stunned silence which then followed it would become still more evident that the 2.7-litre unit intended for use in Jaguars, Fords, Land Rovers, Peugeots and Citroens sounds nothing like a diesel when it's operating under the bonnet of an S-Type. It doesn't even sound like one from a cold start - in that notorious condition you still get an almost entirely clatter-free six-cylinder rumble which creates an impression of unforced elegance which the rest of the car does a very good job of maintaining.Its behaviour is less subdued than its noise. There's a lot of straightline performance available at full throttle, but you can also push on quite smartly with more subtle use of your right foot. I took the second option most of the time, since it allowed me to go as quickly as I felt I needed to.We've already discussed the technical aspects of the engine in a review of the SE version. This particular car is the Sport, which differs from the SE visually in that its exterior trimmings are generally body-coloured rather than chrome. The Sport also has larger wheels - 8x18" alloys rather than 7.5x17" ones - and stiffer suspension, which is optional on the SE, plus more purposeful-looking interior styling.You might imagine that the two cars feel quite different, but in fact there's considerable blurring of the boundaries. The SE, as reported earlier, feels quite sporty considering its emphasis on comfort and luxury, while the Sport wafts more elegantly along A-roads than its specification might lead you to believe.Even though the engine is a lightweight for its type, I suspect this behaviour is partly down to the compensation required in the set-up to carry its bulk (which, I may say, has been achieved very successfully - you don't feel that there is a lot of mass weighing down the front end). Whatever the reason, though, this car feels very much at home when being driven briskly but unfussily along interesting roads. It will corner hard if you want it to, but it doesn't feel as if that is what it was meant to do. The main benefit of the Sport option is to provide slightly more aggressive looks rather than to get from A to B any more quickly than normal.You pay for those looks with the marginally reduced ride comfort created by the effective but uncompromising low-profile Pirelli P Zero tyres, although even here Jaguar has kept the inconvenience to a minimum. Sport suspension or no Sport suspension, the impression is of very smooth ride quality with a layer of surface chatter somewhere in the mix.Unlike the SE, the Sport is available with manual transmission, but the test car was a six-speed automatic, and that was fine by me. The S-Type feels like it was designed to do as much as possible for you, and I'm quite happy to include gearchanging in that list.Everything we've ever said about Jaguar's ability to create a satisfying interior applies here too - it's something that no rival manufacturer can truly match. I flinched slightly at the sight of a button on the centre console to operate the electronic parking brake, having had to deal with far too many hopelessly ill-designed systems of that sort in the last few months, but in this case everything is quite simple, even down to the fact that the brake will release when (but not before) you pull away from a standstill.What with its factory troubles, calamitous US sales, an admission that too many hopes were pinned on the X-Type and the chaos of its Grand Prix involvement, Jaguar has been going through some very hard times. But with the S-Type - and specifically with this particularly good example of the concept - the company is demonstrating that it's still comfortable with its core values, and still knows how to do some things better than almost anyone else.Second opinion: Yes, this is a remarkably quiet-running diesel, and in Sport form a striking car to look at. Most S-Type buyers go for the SE, but the point about the Sport, apart from the mild exterior changes, the different wheels, tyres and suspension settings, is that it has patterned metal trim rather than the classic wood approach which some buyers find a little old-fashioned. I thought that the front seats, while they offer plenty of support, were a little too tight across the shoulders. With this excellent twin-turbo diesel engine, the Sport is suave in performance as well as in appearance, with the much improved 2004 J-gate gear selector, and a far more sensible parking brake arrangement than some of its rivals. Jaguar research shows that potential buyers prefer push-button controls to anything like the BMW i-Drive, and the test car had these in profusion - although many of them are "virtual" touch-screen affairs. I was expecting the ride to be noticeably harsher than on the SE, but that happened only on coarser-surfaced roads, and you can't blame Jaguar for those. Ross Finlay. Engine 2720cc, 6 cylinders Power 203bhp Transmission 6-speed automatic Fuel/CO2 36.0mpg / 208g/km Acceleration 0-62mph: 8.6 seconds Top speed 141mph Price £33,020 Details correct at publication date